The control of automotive engines and the display panels of vehicles require information on the temperature of the engine coolant. Different types of information and different types of electrical signals carrying the information are dictated by the specific uses. Separate sensing devices are commonly mounted on an engine to gather the required data. This requires a hole to be drilled in the engine block and tapped for each device. Aside from the expense of machining the holes, there are expenses involved in wiring harness arrangements to serve each device. Another problem is the lack of room to mount all the needed hardware on an engine. It is proposed, then, to solve the problems by reducing the devices in size or by combining the functions of several devices in one part. This has the advantages of only one hole to machine in the engine block, only one part to maintain in inventory, only one part to install, only one wiring harness to be used and lower price per function.
It has been known to combine a temperature switch and a thermistor in one package, both being grounded through the case so that two terminals are used to provide signals to the hot temperature light and to the analog gage, both on the instrument panel. It is desirable however to include temperature measurement by another thermistor for closed loop fuel control by an electronic control module. Since the thermistors are heat generators the design is critical for a package containing multiple thermistors which yield accurate data.